Incorrect CSS for bold markdown in previews of issues, comments etc. (BB-6224)

When previewing this issue description, the following line

Here is an example of bold in an issue.

renders "bold in bold, but appears as:

Here is an example of
bold
in an issue.

This is a CSS issue where strong elements are having display: block; set by the following stylesheet:

https://dwz7u9t8u8usb.cloudfront.net/m/41d49ff119d6/compressed/css/25ec0da2bbe9.css

/* for headings in form descriptions */
form.aui .field-group strong {
  display: block;
}

which is getting applied to elements in the preview form. The final text renders properly, but it makes previewing bold elements a paint. (Also applies to previewing comment text.)